Radiofrequency window assembly having shielded solder joints and reweldable replacement flanges

ABSTRACT

A radiofrequency window brazed at its periphery to a sleeve by means of solder contained in a groove in the sleeve. The groove is from one-third to one-half the thickness of the window and the diameter of the window is equal to the inside diameter of the sleeve. To provide a shielded solder joint without fillets or voids, the window is held in place during brazing with a pair of snap rings having bevelled faces held against the edges of the window to ensure that solder does not run beyond the edges of the window. The sleeve is mounted within a pair of supporting rings having a pair of truncated conical flanges attached at opposite ends for welding at their outer edges with similar truncated conical flanges attached to respective waveguide flanges. The conical flanges may be cut and rewelded near their outer edges for convenient removal and replacement of the window assembly in a waveguide system.

United States Patent Novajovsky et a1.

[ 1 Oct. 24, 1972 [54] RADIOFREQUENCY WINDOW ASSEMBLY HAVING SHIELDED SOLDER JOINTS AND REWELDABLE REPLACEMENT FLANGES [72] Inventors: William A. Novajovsky; Max W.

Hoelscher, both of Lancaster, Pa.

[731 Assignee: The United States of America as represented by the United States Atomic Energy Commission [22] Filed: Oct. 20, 1970 [21] Appl. No.: 82,379

[52] US. Cl ..333/98 P, 333/97 R, 2 87/189365, 29/4731, 29/600 [51] Int. Cl. .....l-l0lp 1/08, l-l0lp 11/00, B23k 31/02 [58] Field of Search ..333/98 P, 98 R; 29/600, 601, 29/4731, 501, 502; 287/189.365

[56] References Cited UNITED STATES PATENTS 1,890,998 12/1932 Linquist ..285/287 2,050,728 8/1936 Ost ..285/287 2,084,207 6/1937 Linquist et al. ..285/287 X 2,646,995 7/1953 Thompson ..285/287 X 654,131 7/1900 Burke ..29/501 X 2,050,728 8/1936 Ost ..29/501 X 2,376,725 5/1945 Richardson et a1 ..333/98 P 2,523,155 9/1950 Shoupp ..287/l89.365 2,824,289 2/ 1958 Murdock ..333/83 R 3,054,925 9/ 1962 Walter et al ..333/98 P 3,101,461 8/1963 Henry-Bezy et al ..333/98 P Primary Examinerl-lerman Karl Saalbach Assistant Examiner-Wm. H. Punter Attorney-Roland A. Anderson [57] ABSTRACT A radiofrequency window brazed at its periphery to a sleeve by means of solder contained in a groove in the sleeve. The groove is from one-third to one-half the thickness of the window and the diameter of the window is equal to the inside diameter of the sleeve. To provide a shielded solder joint without fillets or voids, the window is held in place during brazing with a pair of snap rings having bevelled faces held against the edges of the window to ensure that solder does not run beyond the edges of the window. The sleeve is mounted within a pair of supporting rings having a pair of truncated conical flanges attached at opposite ends for welding at their outer edges with similar truncated conical flanges attached to respective waveguide flanges. The conical flanges may be cut and rewelded near their outer edges for convenient removal and replacement of the window assembly in a waveguide system.

6 Claims, 4 Drawing Figures RADIOFREQUENCY WINDOW ASSEMBLY HAVING SHIELDED SOLDER JOINTS AND REWELDABLE REPLACEMENT FLANGES BACKGROUND OF THE INVENTION The invention disclosed herein was made under, or in, the course of Subcontract No. 8-169 under Prime Contract No. AT(043 )400 with the US. Atomic Energy Commission.

The present invention relates to a radio-frequency window assembly for a waveguide system, and more particularly, it relates to a window assembly in which all solder joints present little or no profile to direct impingement of electromagnetic radiation and which has reweldable flanges for convenient removal and replacement of the window assembly in the system.

The purpose of a radiofrequency window is to prevent gaseous connection between an evacuated space and a pressurized space and still permit passage of radiofrequency waves, particularly microwaves, from one space to the other, such as at the output of a klystron tube. Generally, such a window is connected by a solder joint at its periphery to the walls of a conduit that is common to both spaces. Great care must be taken in making the solder joint: too little metal in the solder joint produces voids which tend to leak gas between the spaces; a solder joint that is exposed by design or which has too much or too little solder metal exposes the inherently uneven surface of the joint directly to the electromagnetic energy that is transmitted through the spaces and the window. Such surfaces provide field concentration points that result in high electric and magnetic field concentrations at the points during transmission of energy through the window. The field concentrations eventually cause localized breakdown of the joint and/or window. It is desirable therefore to assemble a radiofrequency window so as to eliminate leaks and causes of high field concentrations. It is further desirable that means be provided for convenient and rapid removal and replacement of the window in the waveguide system upon eventual failure of the window.

SUMMARY OF THE INVENTION In brief, the invention pertains to a radiofrequency window assembly that may be simply and rapidly removed and replaced in a waveguide system, that has window solder joints that are free of voids and fillets, and that has all solder joints shielded from direct exposure to electromagnetic radiation that is transmitted through the window. The window is made to have a diameter precisely equal to the inside diameter of a sleeve that is provided with an internal groove that is from one-third to one-half the thickness of the window. The groove is filled with solder and brazed to join the window to the sleeve with a joint that is virtually covered by the thickness of the window, thereby eliminating fillets and voids in the joint. The sleeve is mounted within and soldered to a pair of supporting rings and is connected to the waveguide system by means of thin truncated conical weld flanges soldered to opposing ends of the supporting rings.

The truncated conical flanges of the window assembly are each nested with a mating truncated conical weld flange that extends from a waveguide arm of the system. The nested flanges are welded together at their outer edges to provide a vacuum tight joint at each end of the assembly. These joints may be conveniently cut near the edge for removal of the window assembly and then rewelded at the edge with conical flanges of a new assembly. Clamping means external to the waveguide system and the window assembly are used to firmly hold the window assembly sleeve to flanges that extend from the system waveguide arms to thereby provide a surface through the assembly that is electrically continuous with respect to transmission of microwaves. The welded conical flanges provide easily cut and reweldable vacuum tight joints for the system, while the sleeve provides a continuous electrical path through the assembly for microwaves and also shields all of the solder and weld joints of the assembly from direct electromagnetic radiation.

It is an object of the invention to shield all solder and weld joints in a radiofrequency window assembly from direct electromagnetic radiation.

Another object is to rapidly and conveniently replace a radiofrequency window assembly in a waveguide system.

Another object is to solder a radio-frequency window in an assembly without fillets or voids.

Another object is to eliminate high electric and magnetic field concentrations in a radio-frequency window assembly.

Another object is to eliminate radiofrequency window assembly.

Other objects and advantageous features of the invention will be apparent in a description of a specific embodiment thereof, given by way of example only, to enable one skilled in the art to readily practice the invention, and described hereinafter with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-sectional view of a radio-frequency window assembly connected to a waveguide system according to the invention.

FIG. 2 is a cross-sectional view of the window assembly of FIG. 1 prior to connection to the waveguide system.

FIG. 3 is a cross-sectional view of a solder joint setup between a radiofrequency window and sleeve of the assembly of FIG. 1 prior to brazing of the joint.

FIG. 4 is a cross-sectional view of a flange extending from a waveguide of the system of FIG. 1 prior to its connection to a corresponding flange of the window assembly.

DESCRIPTION OF AN EMBODIMENT Referring to the drawing there is shown in FIG. 1 a radiofrequency window assembly 10 connected to a waveguide system that includes rectangular waveguides 12 and 13. The window assembly 10 is shown in FIG. 2 prior to its connection to waveguides 12 and 13. The assembly 10 includes a circular radio-frequency window l5 soldered to the central section of a cylindrical sleeve 17 by means of a solder joint 19. The joint 19 is made to be free of fillets and voids by means best described with reference to FIG. 3 wherein an expanded view in cross section of a small section of window 15 and sleeve 17 is shown in a solder joint setup prior to brazing of the joint. The joint is made by formleaks in a ing a groove 21 in the inner surface of the sleeve 17. The groove is formed to have a width that is from onethird to one-half the thickness of the window 15, and the window diameter and internal diameter of the sleeve are made to be equal. The groove 21 is filled with a length of solder wire 23 which has been rolled to have a thickness equal to the depth of the groove 21 and a width equal to the width of the groove 21 so that the solder wire substantially fills the groove 21. The window is centered over the groove and is held in place with a pair of snap rings 22 and 24 on either side of the window. Each ring has a slightly beveled face next to the window to forcefully dam the edges of the window and thereby ensure that the solder 23 does not run beyond the edges of the window. The discontinuities (not shown) in the snap rings that enable the rings to be contracted may be filled with a fibrous alumina material after the rings are in place. The solder joint setup is subjected to a brazing process during which the solder is melted to flow in the groove for penetration into and binding with the sleeve and window. After the solder cools thesnap rings are removed. The resulting joint 19 substantially fills the groove and is free of voids thereby eliminating gas leaks through the joint when the window is placed under a differential pressure. The joint 19 is also free of fillets thereby eliminating uneven surfaces which would result in high field concentrations when the window is "subjected to electromagnetic radiation. The joint is further preserved by its being virtually covered by the edge of the window to shield it from direct electromagnetic radiation.

The wall of the sleeve 17 is made thin so as to permit the joint 19 to be brazed with a small amount of heat over a very short period to avoid heat damage to the window 15. The window assembly 10 is further provided with a pair of supporting rings 25 and 26 which are joined as an integral unit by means of a joint 28 that may be conveniently formed by brazing a solder sheet between the rings. The rings 25 support the sleeve 17 near its ends by means of inwardly extending ridges 30 which contact the sleeve near its ends. The rings may be conveniently joined to the sleeve by means of solder joints 32 which are formed at the edges of the ridges 30 and the outer surface of the sleeve 17.

The assembly 10 further includes a pair of thin truncated conical weld flanges 34 and 35 each having a short transverse lip at the truncation. Each flange is soldered along the lip by means of a joint 37 to the outer end of the respective supporting ring.

The window assembly 10 is connected to the waveguide system by means including a second set of truncated conical weld flanges 39 and 40 which nest with the flanges 34 and 35, respectively and which are provided with a short transverse lip at the truncation. The flanges 39 and 40 may be made integral with the waveguides 12 and 13, respectively, by being soldered to window flanges 42 and 43 that extend from the waveguides. The flanges 42 and 43 are each provided with a step in their face to which the lip of the respective conical flanges 39 and 40 may be soldered. The flange 39 is shown in FIG. 4, as being integral with the flange 42 and waveguide 12 prior to connection of the window assembly 10 to the waveguide system.

The connect the window assembly 10 to the waveguide system, the flanges 34 and 39, and 35 and 40 respectively, are brought into nesting contact so that both the inner and outer edges of the mated flanges are aligned. The outer edges of the mating flanges are then welded together to form vacuum tight joints 45.

In order to ensure a continuous and reliable electrical surface between the sleeve 17 and the waveguides l2 and 13, clamping means are provided to securely hold the window assembly 10 to each of the waveguides 12 and 13. The clamping means is comprised of a pair of clamping rings 47 and 48 which are mounted to bear against flanges 42 and 43 respectively and which are drawn together and secured by means of bolts 50 to firmly hold the window assembly between the waveguides 12 and 13..

The length of the sleeve 17 with respect to the combined length of the supporting rings 25 and 26 is such that the transverse surfaces at the ends of the sleeve bear against the faces of the flanges 42 and 43 while the nested conical flanges 34 and 39, and 35 and 40 do not bear against one another. Such an arrangement provides a reliable and continuous electrical connection between the sleeve 17 and the waveguides l2 and 13 with respect to microwaves.

Several pump out holes 52 are provided around the edge of the faces of the flanges 42 and 43. These holes connect to the space that remains between the mated conical flanges so that all spaces connecting to the in terior of the waveguide system may be completely evacuated.

It is noted that the joints 19 and 32 provide vacuum isolation between opposite sides of the window 15, while the joints 45 provide isolation between the interior of the waveguide system and the atmosphere. All of these joints as well as the joint 28 are shielded from direct impingement of electromagnetic radiation by the sleeve l7while the joint 19 is shielded by the window 15.

It is further noted that the thin conical flanges 34 and 39, and 35 and 40, maybe out near their respective joints 45 to remove the window assembly 10 which may be easily replaced with a similar window assembly which requires rewelding only at the edges of the conical flanges 39 and 40 and reclamping between the waveguides 12 and 13.

In an embodiment exemplifying the invention, the sleeve 17 was made of -30 copper-nickel and had an internal diameter of approximately 3 inches, a length of approximately 1.2 inches and walls 0.027 inch thick. The groove 21 had a depth of approximately 0.012 inch and a width of 0.035 inch. The solder wire 23 was a round copper solder wire having a diameter of 0.02 inch before rolling to fit into the groove 21. The window was metallized cobalt-copper plated ceramic window having a diameter and width of approximately 3 inches and 0.091 inch, respectively. The conical flanges 34, 35, 39, and 40 were made of cupro nickel and the edges were heliarc welded. The waveguides l2 and 13 were rectangular and had inside dimensions of 1.34 X 2.84 inches. Microwave energy in the range of 20 MW peak and 20 KW average power at a frequency of 2,856 MHz was passed through the waveguides and window over an extended period. Upon eventual failure of the window, it was replaced with a similar one by cutting and rewelding the welds 45. It is estimated that at least five replacements of the window assembly could be made with the original conical flanges 39 and 40 that extend from the waveguides 12 and 13.

While an embodiment of the invention has been shown and described, further embodiments or combinations of those described herein will be apparent to those skilled in the art without departing from the spirit of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A radiofrequency window assembly for connection in a waveguide system, comprising:

a sleeve having a predetermined internal diameter and an intemai groove formedin the central section of said sleeve, said sleeve diameter being constant over its entire length on each side of said groove;

a radiofrequency window having a diameter equal to the internal diameter of said sleeve and mounted within said sleeve over said groove, said window being centered over said groove and having a thickness that is greater than the width of said groove;

a joint between said window and said sleeve, comprised of solder filling said groove and brazed in said groove to said sleeve and said window, all said solder being entirely between said window and said sleeve, said window shielding all said solder from direct exposure to electromagnetic radiation transmitted through said window; and

means extending from said sleeve for forming a vacuum connection with said waveguide system.

2. The radiofrequency window assembly of claim 1,

wherein the thickness of said window is 2 to 3 times the width of said groove.

3. The radiofrequency window assembly of claim 1, wherein said sleeve has a thin wall and said means extending from said sleeve includes supporting means for said sleeve, and first and second weld flanges extending from said supporting means, and said waveguide system includes first and second waveguide arms, and third and fourth weld flanges extending respectively from said first and second waveguide arms for mating engagement with said first and second flanges respectively, said first and third flanges being welded together at their outer edges to form a vacuum seal, and said second and fourth flanges being welded together at their outer edges to form a vacuum seal.

4. The assembly of claim 3 further including means remote from said sleeve for maintaining the inner surface of said sleeve and the inner surface of said waveguides electrically continuous with respect to microwaves.

5. The assembly of claim 4, wherein said remote means includes first and second window flanges extending from said first and second waveguide arms respectively, said sleeve being mounted between said first and second window flanges, and a pair of clamping rings with said window flanges mounted therebetween, and means for forcing said clamping rings together to firmly hold said sleeve between said window flanges.

6. The assembly of claim 5 wherein said supporting means is a pair of supporting rings brazed to said sleeve for carrying said first and second weld flanges and for supporting said sleeve adjacent the ends of the sleeve near their point of cgnta ct vyith saig window flanges. 

1. A radiofrequency window assembly for connection in a waveguide system, comprising: a sleeve having a predetermined internal diameter and an internal groove formed in the central section of said sleeve, said sleeve diameter being constant over its entire length on each side of said groove; a radiofrequency window having a diameter equal to the internal diaMeter of said sleeve and mounted within said sleeve over said groove, said window being centered over said groove and having a thickness that is greater than the width of said groove; a joint between said window and said sleeve, comprised of solder filling said groove and brazed in said groove to said sleeve and said window, all said solder being entirely between said window and said sleeve, said window shielding all said solder from direct exposure to electromagnetic radiation transmitted through said window; and means extending from said sleeve for forming a vacuum connection with said waveguide system.
 2. The radiofrequency window assembly of claim 1, wherein the thickness of said window is 2 to 3 times the width of said groove.
 3. The radiofrequency window assembly of claim 1, wherein said sleeve has a thin wall and said means extending from said sleeve includes supporting means for said sleeve, and first and second weld flanges extending from said supporting means, and said waveguide system includes first and second waveguide arms, and third and fourth weld flanges extending respectively from said first and second waveguide arms for mating engagement with said first and second flanges respectively, said first and third flanges being welded together at their outer edges to form a vacuum seal, and said second and fourth flanges being welded together at their outer edges to form a vacuum seal.
 4. The assembly of claim 3 further including means remote from said sleeve for maintaining the inner surface of said sleeve and the inner surface of said waveguides electrically continuous with respect to microwaves.
 5. The assembly of claim 4, wherein said remote means includes first and second window flanges extending from said first and second waveguide arms respectively, said sleeve being mounted between said first and second window flanges, and a pair of clamping rings with said window flanges mounted therebetween, and means for forcing said clamping rings together to firmly hold said sleeve between said window flanges.
 6. The assembly of claim 5 wherein said supporting means is a pair of supporting rings brazed to said sleeve for carrying said first and second weld flanges and for supporting said sleeve adjacent the ends of the sleeve near their point of contact with said window flanges. 